Pulping of manila, sisal, or like raw fibrous materials



Patented Apr. 10, 1934 PATENT OFFICE PULPING OF MANILA, SISAL, OR LIKE RAW FIBROUS MATERIALS George A. Richter, Berlin, N. H., assignor to Brown Company, Berlin, N. H., a corporation of Maine No Drawing.

Application February 27, 1932, Serial No. 595,669

Claims. (01. 92-14) This invention relates to the pulping of raw fibrous materials of the nature of manila and sisal. Such raw fibrous material can be pulped successfully with various chemical liquors intopulp is therefore one which, when beaten into a half-stock satisfactory for papermaking, conduces to papers of a hard, translucent character.

Such pulps may hence be desirable in the case of so-called glassine papers, but in the case of many papers the easy hydratability of the pulp and its tendency to make for hardness and translucency are objectionable.

The object of the present invention is to take advantage of the excellent physical qualities, in-

cluding high strength, tear resistance, and fold endurance, which inhere in pulps derived from manila, sisal, and the like, and at the same time to prepare such pulps with a sufficiently low pentosan content to be compatible with proper conditioning in the beater engine for papermaking and the attainment of well-textured papers possessing the opacity and feel attainable I in rag papers. I have found that this can be done if raw manila or sisal undergoes first the action.

39 of a'cooking liquor which removes pentosans or hydrolyzes them into alkali-soluble products, and then the action of a suitable alkaline cooking liquor. The first cooking liquor is preferably a solution of sodium sulphite which may be slightly 5 acid or alkaline. Not only does the sodium sulphite make for a transformation of the pentosans into alkali-soluble products to be removed by subsequent cooking'in an alkaline liquor, but, when the resulting pulp is to be bleached, the

0 sodium sulphite further induces a state of easy bleachability therein. The sodium sulphite, besides extracting ligneous groups in the raw material, evidently militates against such change in alkali in suflicient amount to accomplish the desired removal of pentosans. The alkali may be added directly to the precooked mass of fibrous material and liquor in the digester; or the initial cooking liquor may be drained from the digester and the digested mass, either with or without washing, may then be treated With the alkaline liquor and cooked therein.

I shall now instance a procedure falling within the ambit of the present invention and yielding a pulp having the desired properties. The raw fibrous material, e. g., manila, is first cooked in a closed digester for about one to two hours in a rather dilute solution of sodium sulphite, say one of about 2% strength, at a temperature of about 335 F. Without releasing the pressure in the digester or removing its liquor content, I may then inject thereinto the desired amount of alkali in the form of a concentrated solution, for instance a 50% caustic soda solution. The liquor in the digester may thus be made to contain alkali equivalent to, say, about a 2% caustic soda solution. The cooking may then be continued at. about 335 F. in the digester for about one to two hours, at the end of which time there is produced a pulp which has a pentosan content of about 3% to 8%, which is easily bleachable, and which responds to a conditioning in the beater engine compatible with the attainment of papers of the desired appearance and other physical qualities.

It is surprising that the desired results are not secured by combining the alkali used in the second cooking-step with the sodium sulphite used in the first cooking operation and digesting the raw fibrous material in the single composite cooking liquor. In other words, the alkali evidently works far more effectively when used after the sodium sulphite has performed the function of rendering the pentosans more responsive to removalbyalkali. Indeed, after the cooking in the solution of the sodium sulphite has been completed, comparatively little alkali, as already indicated, need be used for the second step of cooking to bring about the desired results. It is for this reason that such alkali as I employ in my process I preferably put to work after the initial cook in sodium sulphite solution has been effected, little or no free alkali being present in the sodium sulphite solution at the start of cocking therein. Yet, the sulphite solution might well contain some acid, but preferably in slight amount so as not to injure the cellulose fibers. For instance, such weak acids as acetic or carbonic might be added to the sodium sulphite solution. It sulphurous acid even in small amount is used in the sodium sulphite solution, it is necessary to practise the initial cook in an acid-resistant digester. This is hence less preferable, since it is, possible to practise both cooks in a single steel-shell digester of the type customarily used for alkaline cooking.

It is possible to use alkaline liquors from various sources in the practice of the second cooking step, for instance liquors containing sodium carbonate and/or sodium sulphide, such as are available in the recovery systems of a kraft or soda pulp mill. The alkaline liquors may advantageously contain sodium sulphite in amount even exceeding that present in the initial cooking liquor, as this chemical promotes the removal of ligneous matter and hence appreciates the quality of easy bleachability in the resulting pulp. When a strong alkaline liquor, such as is desirable for injection into a digester containing the initially cooked mass and the original liquor residuum, is used, it may well be the concentrated solutions ordinarily prepared from the recovered smelted compounds in a soda or k-raft mill, or the concentrated, causticized liquors subsequently produced and entering into the preparation of fresh cooking liquors.

I have adverted to the use of about 2% sodium sulphite in the initial cooking liquor and the use of about 2% caustic soda equivalent in the secondary cooking liquor. These percentages were mentioned because they lead to the desired kind of pulp product in a reasonably short total cooking period under highly practical temperature. It is, of course, possible to use higher concentrations of chemical, but it is preferable on account of chemical costs to operate with the smallest quantities of chemical consistent with other practical operating factors and the kind of product described. Indeed, the initial cooking operation may be performed in plain water or in a solution of sodium sulphite as weak as about 0.5% concentration. The second cook can take place in a solution of caustic soda of as low as about 1% strength, which may be added to the precooked mass as a relatively concentrated solution also containing, if desired, sufficient sodium sulphite to produce a composite secondary cooking liquor of about 1% caustic soda and, say, about 5% sodium sulphite concentration. The two-stage cooking process of the present invention is hardly of utility when applied to chipped wood, as the wood resists pulping to such an extent that it is inappreciably softened when processed in accordance with my invention under conditions such as would convert raw fibrous materials, such as manila and sisal, into the very pulps herein desired.

I claim:

1. A process of cooking raw fibrous material of the nature of manila and sisal to produce pulp, which comprises initially cooking such material in a substantially neutral solution of a soluble sulphite of less than about 2% strength, to render pentosan groups present therein more responsive to removal by alkali, and then cooking the resulting material in an alkaline liquor to produce a pulp of a pentosan content not exceeding about 8%.

2. A process of cooking raw fibrous material of the nature of manila and sisal to produce pulp, which comprises initially cooking such material under pressure in a substantially neutral solution of sodium sulphite of less than about 2% strength, rendering said liquor distinctly alkaline, and continuing the cooking operation under pressure in the distinctly alkaline liquor. I

3. A process of cooking raw fibrous material of the nature of manila and sisal to produce pulp, which comprises initially cooking such material under pressure in a substantially neutral solution of essentially only sodium sulphite of less than about 2% strength, and then cooking the resulting material under pressure in a solution of alkali of a strength of not less than about 1% caustic soda equivalent.

4. A process of cooking raw fibrous materials of the nature of manila and sisal to produce pulp, which comprises initially cooking such material under pressure in a substantially neutral solution of essentially only sodium sulphite of less than about 2% strength, and then cooking the resulting material under pressure in a solution of alkali of not less than about 1% caustic soda equivalent and containing more active sodium sulphite than that present in the initial cooking liquor.

5. A process of cooking raw fibrous materials of the nature of manila and sisal to produce pulp, which comprises initially cooking such material under pressure in a substantially neutral solution of essentially only sodium sulphite of less than about 2% strength, and then cooking the resulting material under pressure in a solution of alkali of a strength of about 2% caustic soda equivalent.

GEORGE A. RICHTER. 

